1. Field of the Invention
The present invention relates a vibration speaker installed in a communication appliance such as a cellular phone and adapted to conduct both the function for generating sound and the function for generating vibrations. More particularly, the present invention relates to a vibration speaker capable of applying upward and downward damping forces to a vibrating body, thereby reducing a variation in the amplitude of vibrations depending on a variation in frequency to obtain an improvement in vibration characteristics.
2. Description of the Related Art
Generally, a speaker is a sound generating device for outputting an audible sound corresponding to an audio signal electrically or electronically received or a bell or melody previously inputted.
Typically, such a speaker is connected to an audio appliance or amplifier so that it serves as a large-size sound generating means adapted to greatly amplify the amplitude of sound. Alternatively, speakers are widely used which have a greatly reduced size so that they are used as miniature sound generating means.
In particular, speakers applied to miniature communication appliances such as cellular phones or pagers have a greatly reduced size. Such speakers are called xe2x80x9cmicro speakersxe2x80x9d
The current tendency of such micro speakers is toward smaller sizes because communication appliances such as cellular phones are currently intended to have a reduced size or thickness.
FIG. 1 is a sectional view illustrating a conventional micro speaker mainly used in portable communication appliances. As shown in FIG. 1, the conventional micro speaker includes a housing 100 defined with a space therein. A magnet 110 and a voice coil 120 are arranged in the housing 100. The micro speaker also includes a vibrating plate 130 for generating a sound.
In the micro speaker having the above mentioned configuration, when a high frequency current supplied from an external current source is applied to the voice coil 120 via a lead 101, a magnetic field is established in accordance with a cooperation between the voice coil 120 and the magnet 110, thereby causing the voice coil 120 to move vertically. As a result, the vibrating plate 130, which is attached to one end of the voice coil 120, generates a sound while finely vibrating.
The high frequency current applied to the voice coil 120 via the lead 101 is AC. Accordingly, when the magnetic field generated by the voice coil 120 varying in direction in accordance with the direction of the current applied to the voice coil 120 is rendered to correspond to the magnetic field formed by the magnet 110, a repulsion force is exerted between the magnet 110 and the voice coil 120, so that the magnet 110 and the voice coil 120 tend to be moved away from each other. As a result, the voice coil 120 is upwardly moved away from the magnet 110.
On the other hand, when the magnetic field generated by the voice coil 120 has a direction reverse to that of the magnetic field formed by the magnet 110, an attraction force is exerted between the magnet 110 and the voice coil 120, so that the magnet 110 and the voice coil 120 tend to be moved toward each other. As a result, the voice coil 120 is downwardly moved toward the magnet 110.
Thus, the voice coil 120 moves upwardly and downwardly in accordance with a change in direction of the magnetic field generated by the voice coil 120. By virtue of the alternating upward and downward movements of the voice coil 120, the vibrating plate 130 attached to the voice coil 120 vibrates upwardly and downwardly. As the vibrations of the vibrating plate 120 is externally emitted, a sound is generated. Thus, the sound generating function is carried out.
Meanwhile, the portable communication appliance also includes a vibrating means adapted to allow the user to recognize a receiving call by vibrations other than sound.
For such a vibrating means, a vibration motor has been mainly used. Recently, a vibration speaker has been developed which is configured by adding a vibrating function to a speaker having a simple sound generating function.
FIG. 2 is a sectional view illustrating a conventional vibration speaker. As shown in FIG. 2, the vibration speaker has a configuration including a voice coil adapted to generate sound when it receives a high frequency current, and a vibration coil adapted to generate vibrations when it receives a low frequency current.
In detail, this vibration speaker includes a housing 100 adapted to form a casing and defined with a space having a desired size. A yoke 105 is arranged at the central portion of the space defined in the housing 100.
A weight 140 fixed to outer surface of the yoke 105 is elastically supported by a pair of vertically spaced plate springs 150 and 155 each fixedly mounted to the inner peripheral surface of the housing at one end thereof. The plate springs 150 and 155 are also mounted to the upper and lower portions of the yoke 105 to support the yoke 105, respectively.
The upper spring 150 is firmly fitted, at its outer peripheral edge, in a holding groove 100a provided at the upper portion of the inner peripheral surface of the housing 100. The outer peripheral edge of the lower spring 155 is in contact with a step of the housing 100 at its upper surface. The step is formed at the lower portion of the inner peripheral surface of the housing 100. Under the condition in which the lower spring 155 is in contact with the step, the lower spring 155 is bonded to the housing 100 using an adhesive 100b applied between the inner peripheral surface of the housing 100 and the lower surface of the lower spring 155.
A magnet 110 is attached to the central portion of the yoke 105. Beneath the magnet 110, a vibration coil 115 is attached to the upper surface of a lower plate 102 attached to the lower end of the housing 100.
A vibrating plate 130 adapted to generate sound is mounted to the upper end of the housing 100. A voice coil 120 extends downwardly from the vibrating plate 130 in such a fashion that it surrounds the magnet 110.
In order to obtain an increased amplitude of vibrations in the vibration speaker having the above mentioned configuration, a weight 140, which is a mass body, is arranged in the space defined between the plate springs 150 and 155.
In the conventional vibration speaker having the above mentioned configuration, when a high frequency signal is applied to the voice coil 120, the vibrating plate 130 vibrates finely by virtue of electromagnetic forces generated between the voice coil 120 and the magnet 110, thereby generating sound. This sound is used as a speaker sound.
When a low frequency signal is applied to the vibration coil 115, the vibrating body moves upwardly and downwardly by virtue of electromagnetic forces generated between the vibration coil 115 and the magnet 110. This upward and downward movements are transmitted to the housing 100 via the plate springs. Thus, a desired vibration function is carried out.
In the above mentioned conventional vibration speaker, the vibrating body, which is composed of the yoke 105, the magnet 110, and the weight 140, is upwardly and downwardly moved in accordance with a vibration excitement at a desired frequency using the resonant frequency of the vibrating body. Thus, vibrations are generated.
However, this conventional vibration speaker has a disadvantage in that there may be a variation in the amplitude of vibrations due to an assembling dispersion of the yoke 105, magnet 110, and weight 140 included in the vibrating body, and that there is a deviation between the designed resonant frequency of the vibrating body and the actual resonant frequency of the vibrating body because a variation in the amplitude of vibrations occurs depending on the dimension dispersion of each element included in the vibration speaker.
Referring to FIG. 3, it can be found that the gradient of peak at resonance is appeared in a large scale. As mentioned above with reference to FIG. 2, FIG. 4 shows that there is a touching phenomenon between a weight and a lower plate at region of resonant frequency during oscillation of the weight. Therefore vibration characteristics of the conventional art is not good.
For example, where the mass of the vibrating body is varied by 0.03 g, the resonant frequency is shifted by about 1 Hz. When the resonant frequency is shifted by 1 to 2 Hz, the amplitude of vibrations is considerably reduced. For this reason, there is a problem in that it is difficult to induce desired vibration characteristics.
The resonant frequency may be expressed by the following equation:
Fn=1/(2xcfx80)(k/m)
where, k represents a spring constant, and m represents a mass.
Referring to the above equation, it can be found that the resonant frequency Fn is varied, depending on a variation in the mass m.
Furthermore, the effective space allowing the vibrating body to move upwardly and downwardly is considerably restricted in the above mentioned convention vibration speaker because the speaker has a thin structure. For this reason, the vibrating body may come into contact with the upper and lower surfaces of the housing 100 during its upward and downward movements when the amplitude of the vibrating body exceeds a predetermined level due to a variation in the weight of the vibrating body. As a result, there may be a degradation in vibration characteristics. In addition, noise may be generated. There may also be a reduction in the life of the product.
As depicted in the graphs, the maximum effective amplitude of vibrations should be maintained at about 2.5 G, taking into the consideration the restricted effective space in which the vibrating body moves upwardly and downwardly. In the conventional vibration speaker, however, the maximum effective amplitude of vibrations reaches 3.5 G. As a result, the vibrating body is struck against the upper and lower surfaces of the shield plate 102, thereby generating noise. Due to frequent striking of the vibrating body, the durability of the speaker is degraded.
Moreover, the frequency band of vibrations practically usable corresponds to the frequency range in which the vibrating body does not come into contact with the shield plate 102. As a result, the effective frequency band of vibrations is reduced toward the left or right range from the resonant frequency of 182 Hz. This means that it is impossible to obtain a desired vibration function. Also, there is a disadvantage in that the touch of vibrations is bad.
Therefore, an object of the invention is to provide a vibration speaker capable of applying a damping force to a plate spring adapted to support a vibrating body, thereby reducing a variation in the amplitude of vibrations depending on a variation in frequency to obtain stable vibration characteristics.
Another object of the invention is to provide a vibration speaker capable of preventing elements included in the vibration speaker from being struck against one another during the execution of a desired vibration function, thereby achieving an improvement in durability to extend the lift of the vibration speaker.
In accordance with the present invention, these objects are accomplished by providing a vibration speaker comprising: a housing having a hollow cylindrical structure opened at both ends thereof, the housing being attached, at one end thereof, with a vibrating plate adapted to generate sound and, at the other end thereof, with a shied plate adapted to shield the other end of the housing; a yoke centrally arranged in the interior of the housing and fixedly mounted to an inner peripheral surface of the housing by plate springs spaced apart from each other by a desired distance; a magnet attached to an upper end of the yoke to have N and S poles vertically aligned together, the magnet constituting a magnetic circuit; a voice coil having an upper end fixed to the vibrating plate, and a lower end arranged adjacent to the magnet; a vibration coil attached to one surface of the shield plate while facing the magnet; and damping means arranged at the inner peripheral surface of the housing and adapted to apply a damping property to the plate springs, thereby reducing a variation in the amplitude of vibrations transmitted to the plate springs.
The damping means may comprise a rubber member composed of a rubber material to respective outer peripheral ends of the plate springs.
The damping means may comprise soft bonds applied in a desired amount to respective outer peripheral ends of the plate spring fixedly mounted to the inner peripheral surface of the housing.
The vibration speaker may further comprises a weight attached to an outer peripheral surface of the yoke, the weight having a desired mass.